The present invention relates to an air filter, especially an air filter which can efficiently catch a carbon dust.
As an air filter for vehicles, a wet type filter made up of paper impregnated with oil is known. Typically, viscous oil is used as impregnating oil, and such a filter is called a xe2x80x9cviscous-typexe2x80x9d air filter as a popular name. The viscous-type air filter has the merit of lengthening its lifetime as compared to a dry type filter which is not impregnated with oil. In the viscous-type air filter, the function of absorbing an other dust particle to a surface of a dust particle is generated because an absorbed dust particle is impregnated with oil after this particle is absorbed to a surface of the filter. In such a mechanism, since the dust particles can be caught one after another, absorption ability per a volume of the filter is increased.
And, an improved viscous type air filter is mentioned in Japanese utility model publication No. S63-27767. In the air filter mentioned in Japanese utility model publication No. S63-27767, the first filter member having comparably high density and the second filter member having comparably low density are laminated. Because of applying such a laminating construction, the rate of oil impregnation of the first filter member is made different from that of the second filter member, and accordingly, clogging of the filter is prevented so that the dust is efficiently caught.
However, there is the fault that a carbon dust can not be efficiently caught by the wet type filter impregnated with oil. On the other hand, the carbon dust can be efficiently caught by using the dry type filter which is not impregnated with oil, but there is the fault that the lifetime of the filter comes to be shortened in the case where a filter paper is used Furthermore, the cost is unfortunately increased in the case where non woven fabric is used alone.
It is an object of the present invention to provide an air filter in which the carbon dust can be efficiently caught and the cost can be lowered.
The air filter of the present invention comprises a first filter layer impregnated with oil; an oil repellent layer disposed in the downstream side of the first filter layer, having the property of repelling the oil; and a second filter layer disposed in the downstream side of the oil repellent layer, impregnated with no oil. And the transfer of the oil to the second filter layer is controlled by the oil repellent layer.
According to the invention, because the oil of the first filter layer is repelled by the oil repellent layer, the oil is hardly transferred to the second filter layer. Accordingly, the performance of the second filter layer impregnated with no oil is fully displayed.
In the above air filter, a carbon dust may be caught by the second filter layer.
In this case, because the oil of the first filter layer is repelled by the oil repellent layer, the oil is hardly transferred to the second filter layer. Accordingly, the performance of the second filter layer impregnated with no oil is fully displayed so that the carbon dust can be efficiently caught.
In the above air filter, the first filter layer and the oil repellent layer may be integrated so as to be formed as an integral layer.
In this case, because the first filter layer and the oil repellent layer can be formed as a layer, the construction of the layers can be made simple and the thickness of the whole filter can be made small.
In the above air filter, the oil repellent layer may be formed by coating an oil repellent agent on a surface of the integral layer.
In this case, the oil repellent layer can be formed by a simple process.
In the above air filter, pores of the second filter layer may be more coarse than pores of the first filter layer.
In this case, the influence of the second filter layer to the pressure loss is reduced and the pressure lose of the whole filter can be suppressed.
In the above air filter, the second filter layer may compose one of a non woven fabric and a filter paper.
In this case, because the second filter layer comprises a non woven fabric or a filter paper, the carbon dust can be efficiently caught by contact filtration.
In the above air filter, the air filter may be capable of being attached to an intake path of an engine.
In this case, the carbon dust can be efficiently removed from the intake air of the engine. And, inhalation of the oil to the engine can be prevented.